Physical conditions of a tire including an air pressure in a tire have to be checked for safety traveling of a vehicle. It takes time and effort for a man to check tires. A tire monitoring system for automatically detecting physical conditions of a tire including an air pressure in a tire has been developed and become available for passenger vehicles.
The tire monitoring system includes a sensor generally fixed to a tire for detecting physical conditions of the tire and transmitting the detected result wirelessly, and a monitor for receiving the data sent from the sensor.
The sensor is generally provided inside a tire usually by being fixed to the rim of the tire or built in the tire.
A sensor with a function of storing historical information including manufacturing or repairing of a tire is also known. This type of sensor is usually built in a tire to avoid tampering of stored information.
A tire monitoring system that can be used for automating stability control in traveling of a vehicle has also been developed. In this tire monitoring system, a tire is provided with a sensor having a sensor unit for detecting physical conditions other than an air pressure, such as distortion, the number of revolutions, and rotation angle speed of a tire during the traveling.
“TREAD law (Transportation Recall Enhancement, Accountability and Document Act)” came into effect on November, 2000 in the United States, and “a partial amendment of Road Trucking Vehicle Law (amended Road Trucking Vehicle Law)” came into effect on July, 2002 in Japan.
The TREAD law stipulates outlines of a safe vehicle including more duty to inform a recall or more stringent penalties of negligence of the duty, more detailed items in a quality label of a tire, duty to be equipped with a tire air pressure alarm and improvement of child seats. To meet the duty to be equipped with a tire air pressure alarm stipulated by TREAD law, various manufacturers are manufacturing and selling sensors and tire monitoring systems.
The sensor disclosed in National Publication of International Patent Application No. 8-505939 is known as a conventional example of sensor.
The remote tire pressure monitoring system disclosed in National Publication of International Patent Application No. 8-505939 is a system for displaying a low tire pressure in a vehicle, wherein each tire has a transmitter with its own code, and wherein a central receiver in the vehicle identifies a code of each transmitter. The system is revised so that it restudies the position of a transmitter when a tire is changed while a vehicle is on the way to a destination or getting serviced. When an ASIC encoder in each transmitter is manufactured, it is programmed to send the information with different periods according to its own code in order to avoid crashing wireless frequencies between more than two transmitters on a vehicle.
However, as tire monitoring systems have not had a unified technical standard, the specification of the system varies among manufacturers.
For example, an identification code of a transmitter is 12 bits, 20 bits or 24 bits in conventional systems. For a different identification code, a receiving process at the receiving side also differs.
As another example, a format of transmitted data also varies among manufacturers as shown in FIGS. 20 and 21. Transmitted data 10 in a sensor from company A shown in FIG. 20 includes binary 13 bits including header information 11 consisting of four bits 11a-11d, equipment code 12 consisting of one bit, identification code 13 consisting of three bits 13a-13c, air pressure information 14 consisting of one bit, temperature information 15 consisting of one bit, battery voltage information 16 consisting of one bit, status information 17 consisting of one bit, and control code 18 consisting of one bit.
Transmitted data 20 in a sensor from company B shown in FIG. 21 includes binary 20 bits including header information 21 consisting of four bits 21a-21d, a control code 22 consisting of one bit, an equipment code 23 consisting of one bit, an identification code 24 consisting of four bits 24a-24d, air pressure information 25 consisting of three bits 25a-25c, temperature information 26 consisting of three bits 26a-26c, battery voltage information 27 consisting of three bits 27a-27c, and status information 28 consisting of one bit.
Positions of LSB and MSB may reverse in multiple bits of data of arbitrary information for some manufacturers.
For example, as shown in FIG. 22, the top bit of four bits binary data is LSB and the fourth bit from the top represents MSB in transmitted data employed by company C. In this case, when binary data is “1010”, its hexadecimal value is “5”.
On the other hand, as shown in FIG. 23, the top bit of four bits binary data is MSB and the fourth bit from the top represents LSB in transmitted data employed by company D. In this case, when binary data is “1010”, its hexadecimal value is “A (decimal value: 10)”.
Moreover, the different modulation method is used when the transmission involves radio waves.
A transmission method between a sensor and a monitor varies among manufacturers as stated above. This made a problem when a tire is replaced with another tire embedded with a sensor from a manufacturer different from that embedded in the first tire in such a case as a flat tire. The sensor in the tire to be used is unable to communicate with a monitor used to communicate till then. This required replacement of the entire system.
In view of the above problem, the object of the present invention is to provide a tire monitoring system, its monitor receiver, a monitor and a sensor for monitoring conditions of a tire even when a tire is replaced with another tire fixed with a sensor employing a transmission method different from that employed by a monitor.